The understanding of the role of metal ions in blood coagulation has been a long term goal of this laboratory. To further the understanding of the structure-function relationships of the Gamma-carboxyglutamic acid residues in prothrombin to the metal liganding processes of the protein we will study a naturally occurring variant of prothrombin which contains only three Gamma-carboxyglutamic acid residues. Normal prothrombin contains ten Gamma-carboxyglutamic acid residues. We will correlate the sequence position of the Gamma-carboxyglutamic acid residues in the variant with its metal binding and conformational properties using amino acid sequence analysis, state rate dialysis, fluorescence spectroscopy and conformation specific antibodies. The results of these analyses will be used to compare and contrast the properties of normal prothrombin and the variant prothrombin. Platelets secrete Ca(II) upon activation. There is potential for a significant increase in Ca(II) concentration at the site of platelet plug formation. In addition, Ca(II) dependent conversion of several plasma zymogens may occur on the platelet surface. We will use monoclonal conformation specific antibodies to identify platelet surface antigens whose conformations are altered depending on the presence or absence of metal ligands. We will correlate the presence of the antigen to the status of the platelet (native or activated). We will identify a possible receptor function for the platelet surface antigens recognized by these monoclonal antibodies. Finally we have identified a novel cleavage product of human prothrombin in plasma, fragment 1.2.3. We will access a potential regulatory role for this fragment in hemostasis. There is currently heightened interest in understanding the processes that regulate hemostasis and thrombosis. The studies outlined in this proposal address these biologically interesting and medically important questions.